1. Field of the Invention
The present invention relates to a data processing apparatus that stores input image data and processes the image data such as for printing, image communication, and facsimile communication.
2. Description of the Related Art
In a data processing apparatus with a copy function for electronically scanning and reading an image on a document and copying image data, several functions have been further combined in recent years. For example, such a data processing apparatus may have the following functions: a network printer function for connecting to a network such as a LAN, receiving image data from an information processing apparatus such as a personal computer, and printing an image; a network scanner function for reading image data and transmitting the image data to an information processing apparatus; and a facsimile function for transmitting and receiving image data to and from an external facsimile machine via a network or a telephone line.
A multifunctional data processing apparatus includes a storage device for temporarily storing input image data. Various types of storage devices exist, including those made of semiconductor memory and those implemented as a magnetic storage medium such as a hard disk device. These storage devices allow efficient processing of a large amount of image data and a plurality of jobs.
In a data processing apparatus, semiconductor memory with a fast read/write capability is used as local memory for storing image data being processed, and a hard disk device is used for temporarily saving image data to be processed. Input image data is subjected to image processing such as compression in the local memory and then temporarily saved in the hard disk device. When the turn comes for the image data to be processed, the saved image data is read and subjected to image processing such as decompression in the local memory. The image data is further subjected to desired processing such as printing, image communication, or facsimile communication, and then output to the outside.
When sensitive data is processed in such a data processing apparatus, security measures are taken. For example, on completion of the processing, the image data in the hard disk device is erased or overwritten with random data as described in Japanese Patent Laid-Open No. 9-284572. Further, the erasure is repeated several times as described in Japanese Patent Laid-Open No. 2004-7059. Thus, the image data saved in the hard disk device is made completely unreadable and is invalidated.
For local memory implemented using volatile memory, new image data is stored by overwriting old image data with the new image data. When the power supply for the local memory is shut off, the image data is erased. However, in the case where the data processing apparatus is used round-the-clock, the power is always on and therefore the local memory always contains image data.
Here, a fault may occur in the data processing apparatus due to a noise or an incorrectly sensed document, resulting in that image data input may get out of order, or image data input may be falsely detected although no image data is input. Then, processing goes on without overwriting the old image data stored in the local memory. This causes a problem, for example, that the previously input image is printed, and gives the user security concern.
In the light of the above issues, the object of the present invention is to provide a data processing apparatus that invalidates image data in local memory to prevent leakage of old image data in the event of a fault.